1. Field of the Invention
The invention relates to a thin film magnetic head having at least an inductive magnetic transducer for writing and a method of manufacturing the same.
2. Description of the Related Art
Recently, an improvement in performance of a thin film magnetic head has been sought in accordance with an increase in a surface recording density of a hard disk drive. A composite thin film magnetic head, which has a stacked structure comprising a recording head having an inductive magnetic transducer for writing and a reproducing head having a magnetoresistive (hereinafter referred to as MR) element for reading, is widely used as the thin film magnetic head.
Factors that determine the performance of the recording head include a throat height (TH). The throat height refers to a length (height) of a magnetic pole between an air bearing surface and an edge of an insulating layer for electrically isolating thin film coils for generating a magnetic flux. The air bearing surface refers to a surface of the thin film magnetic head facing a magnetic recording medium and is sometimes called a track surface. A reduction in the throat height is desired for the improvement in the performance of the recording head. The throat height is controlled in accordance with an amount of polishing of the air bearing surface.
An increase in a recording density of the performance of the recording head requires the increase in a track density of the magnetic recording medium. For this purpose, it is necessary to realize the recording head having a narrow track structure. In this structure, a bottom pole and a top pole, which are formed on the bottom and top of a write gap sandwiched between the bottom pole and the top pole, have a narrow width of from a few microns to the submicron order on the air bearing surface. Semiconductor processing technology is used in order to achieve this structure.
An example of a method of manufacturing the composite thin film magnetic head will be now described as an example of a conventional method of manufacturing the thin film magnetic head with reference to FIGS. 43 to 48.
In the manufacturing method, first, as shown in FIG. 43, an insulating layer 102 made of, for example, alumina (Al2O3) is deposited with a thickness of about 5 xcexcm to 10 xcexcm on a substrate 101 made of, for example, altic (Al2O3 and TiC). Then, a bottom shield layer 103 for the reproducing head is formed on the insulating layer 102. Then, for example, alumina is sputter deposited with a thickness of 100 nm to 200 nm on the bottom shield layer 103, whereby a shield gap film 104 is formed. Then, an MR film 105 for constituting the MR element for reproducing is formed with a thickness of a few tens of nanometers on the shield gap film 104, and the MR film 105 is patterned into a desired shape by high-accuracy photolithography. Then, a lead layer (not shown) for functioning as a lead electrode layer electrically connected to the MR film 105 is formed on both sides of the MR film 105. Then, a shield gap film 106 is formed on the lead layer, the shield gap film 104 and the MR film 105, whereby the MR film 105 is buried in the shield gap films 104 and 106. Then, a top shield-cum-bottom pole (hereinafter referred to as a bottom pole) 107 made of a magnetic material for use in both of the reproducing head and the recording head, e.g., permalloy (NiFe) is formed on the shield gap film 106.
Then, as shown in FIG. 44, a write gap layer 108 made of an insulating film, e.g., an alumina film is formed on the bottom pole 107, and a photoresist layer 109 is formed into a predetermined pattern on the write gap layer 108 by high-accuracy photolithography. Then, first-layer thin film coils 110 made of, for example, copper (Cu) for an inductive recording head are formed on the photoresist layer 109 by plating, for example. Then, a photoresist layer 111 is formed into a predetermined pattern by high-accuracy photolithography so as to coat the photoresist layer 109 and the coils 110. Then, heat treatment takes place at a temperature of, for example, 250xc2x0 C. in order to flatten the coils 110 and provide insulation among the coils 110. Then, second-layer thin film coils 112 made of, for example, copper are formed on the photoresist layer 111 by plating, for example. Then, a photoresist layer 113 is formed into a predetermined pattern on the photoresist layer 111 and the coils 112 by high-accuracy photolithography. Then, heat treatment takes place at a temperature of, for example, 250xc2x0 C. in order to flatten the coils 112 and provide insulation among the coils 112.
Then, as shown in FIG. 45, the write gap layer 108 is partially etched at the rear of the coils 110 and 112 (on the right side in FIG. 45) in order to form a magnetic path, whereby an opening 108A is formed. Then, a top yoke-cum-top pole (hereinafter referred to as a top pole) 114 made of a magnetic material for the recording head, e.g., permalloy is selectively formed on the write gap layer 108 and the photoresist layers 109, 111 and 113. The top pole 114 is in contact with and magnetically coupled to the bottom pole 107 in the above-mentioned opening 108A. Then, the write gap layer 108 and the bottom pole 107 are etched by about 0.5 xcexcm by ion milling using the top pole 114 as a mask. Then, an overcoat layer 115 made of, for example, alumina is formed on the top pole 114. Finally, a slider is machined, whereby a track surface (air bearing surface) 120 of the recording head and the reproducing head is formed. As a result, the thin film magnetic head is completed.
FIGS. 46 to 48 show the structure of the completed thin film magnetic head. FIG. 46 shows a cross section of the thin film magnetic head perpendicular to the air bearing surface 120. FIG. 47 shows an enlarged view of a cross section of the magnetic pole parallel to the air bearing surface 120. FIG. 48 shows a plan view. FIGS. 43 to 46 correspond to a cross section viewed from the direction of the arrows along the line A-AA of FIG. 48. The overcoat layer 115 is not shown in FIGS. 46 to 48.
To improve the performance of the thin film magnetic head, it is important to precisely form the throat height TH, an apex angle xcex8, a pole width P2W and a pole length P2L shown in FIGS. 46 and 47. The apex angle xcex8 refers to an angle between a straight line connecting corners of side surfaces of the photoresist layers 109, 111 and 113 on the side of the track surface and a top surface of the top pole 114. The pole width P2W defines a write track width on the recording medium. The pole length P2L represents the thickness of the magnetic pole. In FIGS. 46 and 48, a xe2x80x98TH0 positionxe2x80x99 refers to an edge of the photoresist layer 109 that is the insulating layer for electrically isolating the thin film coils 110 and 112, on the side of the track surface. The TH0 position indicates a reference position 0 of the throat height TH.
As shown in FIG. 47, the structure, in which the respective side walls of parts of the top pole 114, the write gap layer 108 and the bottom pole 107 are vertically formed in self-alignment, is called a trim structure. The trim structure can prevent the increase in an effective track width resulting from a spread of the magnetic flux generated during writing data on a narrow track. As shown in FIG. 47, a lead layer 121 for functioning as the lead electrode layer electrically connected to the MR film 105 is provided on both sides of the MR film 105. The lead layer 121 is not shown in FIGS. 43 to 46.
FIG. 49 shows a plan structure of the top pole 114. As shown in FIG. 49, the top pole 114 has a yoke portion 114A occupying most of the top pole 114, and a pole chip portion 114B having a substantially constant width W1 as the pole width P2W. An outer edge of the yoke portion 114A forms an angle xcex1 with the surface parallel to the air bearing surface 120 at a coupling portion (or junction) between the yoke portion 114A and the pole chip portion 114B. The outer edge of the pole chip portion 114B forms an angle xcex2 with the surface parallel to the air bearing surface 120 at the above-mentioned coupling portion. In this case, a is, for example, about 45 degrees, and i is 90 degrees. The width of the pole chip portion 114B defines the write track width on the recording medium. The pole chip portion 114B includes a portion F in front of the TH0 position (on the side of the air bearing surface 120) and a portion R at the rear of the TH0 position (on the side of the yoke portion 114A). As can be seen from FIG. 46, the portion F extends on the flat write gap layer 108, and the portion R and the yoke portion 114A extend on a coil portion (hereinafter referred to as an apex portion) which is coated with the photoresist layers 109, 111 and 113 and rises mountainously.
The shape of the top pole is described in Japanese Patent Laid-open No. Hei 8-249614, for example.
The pole width P2W is required to be precisely formed in order to determine the track width of the recording head. More particularly, microfabrication for reducing the pole width P2W of the top pole to 1.0 xcexcm or less in dimension has been recently required in order to enable recording at high surface density, that is, in order to form the recording head having the narrow track structure.
Frame plating is used as a method of forming the top pole, as disclosed in Japanese Patent Laid-open No. Hei 7-262519, for instance. To form the top pole 114 by using frame plating, a thin electrode film made of, for example, permalloy is first formed over the apex portion by sputtering, for example. Then, the electrode film is coated with a photoresist, and the photoresist is patterned by photolithography, whereby a frame for plating is formed. Then, the top pole 114 is formed by means of plating by using the preformed electrode film as a seed layer.
On the other hand, a difference in height between the apex portion and the other portions is 7 xcexcm to 10 xcexcm or more, for example. The apex portion is coated with the photoresist with a thickness of 3 xcexcm to 4 xcexcm. Assuming that the photoresist on the apex portion requires a film thickness of 3 xcexcm or more at the minimum, a photoresist film having a thickness of, for example, 8 xcexcm to 10 xcexcm or more is formed under the apex portion because the photoresist having fluidity collects at the lower place.
In order to form the narrow track as described above, it is necessary to form a frame pattern of about 1.0 xcexcm in width by the photoresist film. That is, a micro pattern of 1.0 xcexcm or less in width must be formed by the photoresist film of 8 xcexcm to 10 xcexcm or more in thickness. However, it is very difficult for a manufacturing process to form such a thick photoresist pattern with a narrow pattern width.
Moreover, during exposure for photolithography, a light for the exposure is reflected by an underlying electrode film serving as the seed layer, and the photoresist is exposed to the reflected light. This causes a deformation or the like in the photoresist pattern, and thus a sharp and precise photoresist pattern cannot be obtained. Consequently, the top pole cannot be formed into a desired shape, e.g., the side wall of the top pole becomes round in shape. More particularly, when an attempt is made to further reduce the pole width P2W to W1A as shown in FIG. 50, it is further difficult to obtain the desired width W1A. This is caused for the following reason. In the portion R of the pole chip portion 114B extending on the apex portion, the returned light reflected by the underlying electrode film includes not only the vertically reflected light but also the light reflected obliquely or transversely from an inclined surface of the apex portion. As a result of these reflected lights having an influence upon the exposure of the photoresist layer, a photoresist pattern width for defining the pole width P2W is larger than an intended value. As a consequence, the shape of the portion R becomes the shape shown by a broken line in FIG. 50. The width of the portion F of the pole chip portion 114B in front of the TH0 position is a very important factor for defining the track width on the recording medium. Thus, when the width of the portion F is larger than the above-mentioned value W1A, an intended minute track width cannot be obtained.
The same problem exists in the magnetic head described in Japanese Patent Laid-open No. Hei 8-249614 mentioned above. In the magnetic head described in this publication, the pole width is gradually changed from the TH0 position toward the yoke portion. Thus, the light reflected obliquely or transversely from the inclined surface of the apex portion has an influence upon the exposure of the photoresist layer. Because of the influence, the width of the portion in front of the TH0 position cannot be precisely controlled.
Moreover, as shown in FIG. 50, the portion R of the pole chip portion 114B between the TH0 position and the portion coupled to the yoke portion 114A has substantially the same width as the width of the portion F in front of the TH0 position, and thus the portion R has a small cross-sectional area. Thus, the magnetic flux from the yoke portion 114A is saturated in the portion R, and therefore the magnetic flux cannot sufficiently reach to the portion F for defining the track width. Thus, the following problem exists. Overwrite properties, i.e., the properties of overwriting data on data already written on the recording medium is as low as about 10 dB to 20 dB, for example. Consequently, sufficient overwrite properties cannot be ensured.
The invention is designed to overcome the foregoing problems. It is an object of the invention to provide a thin film magnetic head and a method of manufacturing the same which can precisely control a pole width and can obtain sufficient overwrite properties even when the pole width is reduced.
A thin film magnetic head of the invention comprises: at least two magnetic layers magnetically coupled to each other and having a side facing a recording medium, a part of the side including two magnetic poles facing each other with a gap layer in between; and a thin film coil portion located between the at least two magnetic layers with an insulating layer in between, wherein at least one of the two magnetic layers includes a first magnetic layer portion extending from a recording-medium-facing surface facing the recording medium to or to near an edge of the insulating layer on the side of the recording-medium-facing surface and having a constant width for defining a write track width on the recording medium; a second magnetic layer portion magnetically coupled to the first magnetic layer portion at a first coupling portion located at or near the edge of the insulating layer; and a third magnetic layer portion magnetically coupled to the second magnetic layer portion on the opposite side of the first coupling portion between the first and the second magnetic layer portions, a step along the width is formed at the first coupling portion so that the width of the first magnetic layer portion at the first coupling portion between the first magnetic layer portion and the second magnetic layer portion is smaller than the width of the second magnetic layer portion at the first coupling portion, and a step along the width is formed at a second coupling portion so that the width of the second magnetic layer portion at the second coupling portion between the second magnetic layer portion and the third magnetic layer portion is smaller than the width of the third magnetic layer portion at the second coupling portion.
A method of manufacturing a thin film magnetic head of the invention comprises the steps of forming at least two magnetic layers magnetically coupled to each other and having a side facing a recording medium, a part of the side including two magnetic poles facing each other with a gap layer in between; and forming a thin film coil portion located between the at least two magnetic layers with an insulating layer in between, wherein at least one of the two magnetic layers is formed so as to include a first magnetic layer portion extending from a recording-medium-facing surface facing the recording medium to or to near an edge of the insulating layer on the side of the recording-medium-facing surface and having a constant width for defining a write track width on the recording medium; a second magnetic layer portion magnetically coupled to the first magnetic layer portion at a first coupling portion located at or near the edge of the insulating layer; and a third magnetic layer portion magnetically coupled to the second magnetic layer portion on the opposite side of the first coupling portion between the first and the second magnetic layer portions, a step along the width is formed at the first coupling portion so that the width of the first magnetic layer portion at the first coupling portion between the first magnetic layer portion and the second magnetic layer portion is smaller than the width of the second magnetic layer portion at the first coupling portion, and a step along the width is formed at a second coupling portion so that the width of the second magnetic layer portion at the second coupling portion between the second magnetic layer portion and the third magnetic layer portion is smaller than the width of the third magnetic layer portion at the second coupling portion.
In the thin film magnetic head or the method of manufacturing the same of the invention, the write track width on the recording medium is defined by the constant width of the first magnetic layer portion. The first magnetic layer portion is magnetically coupled to the second magnetic layer portion having the larger width than the width of the first magnetic layer portion at or near the edge of the insulating layer on the side of the recording-medium-facing surface. The step along the width is formed at the first coupling portion. The second magnetic layer portion is magnetically coupled to the third magnetic layer portion having the larger width than the width of the second magnetic layer portion on the side of the second magnetic layer portion opposite to the first coupling portion between the first and second magnetic layer portions. The step along the width is formed at the second coupling portion.
In the thin film magnetic head or the method of manufacturing the same of the invention, a step face of the second magnetic layer portion at the first coupling portion may be substantially perpendicular to a direction in which the first magnetic layer portion extends.
In the thin film magnetic head or the method of manufacturing the same of the invention, the edges of the step face of the second magnetic layer portion along the width may be chamfered.
In the thin film magnetic head or the method of manufacturing the same of the invention, the width of the second magnetic layer portion may be substantially fixed regardless of the position thereof.
In the thin film magnetic head or the method of manufacturing the same of the invention, the width of the second magnetic layer portion may vary according to the position thereof.
In the thin film magnetic head or the method of manufacturing the same of the invention, the width of the second magnetic layer portion may become larger as it is farther from the first coupling portion.
In the thin film magnetic head or the method of manufacturing the same of the invention; a step face of the third magnetic layer portion at the second coupling portion may be substantially perpendicular to a direction in which the second magnetic layer portion extends.
In the thin film magnetic head or the method of manufacturing the same of the invention, the width of the third magnetic layer portion may be substantially fixed regardless of the position thereof.
In the thin film magnetic head or the method of manufacturing the same of the invention, the width of the third magnetic layer portion may vary according to the position thereof.
In the thin film magnetic head or the method of manufacturing the same of the invention, the width of the third magnetic layer portion may become larger as it is farther from the second coupling portion.
In the thin film magnetic head or the method of manufacturing the same of the invention, the one magnetic layer may further include a fourth magnetic layer portion magnetically coupled to at least a part of the first magnetic layer portion, the second magnetic layer portion or the third magnetic layer portion and having the larger width and area than the width and area of the third magnetic layer portion.
In the thin film magnetic head or the method of manufacturing the same of the invention, the first magnetic layer portion, the second magnetic layer portion and the third magnetic layer portion may be integrally formed by the same step.
In the thin film magnetic head or the method of manufacturing the same of the invention, the first magnetic layer portion, the second magnetic layer portion, the third magnetic layer portion and the fourth magnetic layer portion may be integrally formed by the same step.
In the thin film magnetic head or the method of manufacturing the same of the invention, the first magnetic layer portion, the second magnetic layer portion and the third magnetic layer portion may be integrally formed by the same step, and the fourth magnetic layer portion may be formed as a separate part by a different step from the step of forming the first magnetic layer portion, the second magnetic layer portion and the third magnetic layer portion.
In the thin film magnetic head or the method of manufacturing the same of the invention, the fourth magnetic layer portion may extend so as to overlap at least a part of the first magnetic layer portion, the second magnetic layer portion or the third magnetic layer portion.
In the thin film magnetic head or the method of manufacturing the same of the invention, the fourth magnetic layer portion may extend so as to overlap a part of the first magnetic layer portion across the first coupling portion between the first and second magnetic layer portions, and an edge face of the fourth magnetic layer portion at the overlapping portion on the side of the recording-medium-facing surface may be perpendicular to the direction in which the first magnetic layer portion extends. In this case, the coupling portion between the first and second magnetic layer portions is recessed relative to the edge face of the fourth magnetic layer portion. Therefore, even if corners of the step along the width at the coupling portion are round in shape, the width of the first magnetic layer portion for defining the write track width on the recording medium is exactly fixed over the whole region between the perpendicular portion and the end portion. Furthermore, the position of the edge face of the fourth magnetic layer portion may match the position of the edge of the insulating layer on the side of the recording-medium-facing surface-facing surface. In this case, the width of the first magnetic layer portion for defining the write track width on the recording medium is exactly fixed over the whole region called a throat height.
In the thin film magnetic head or the method of manufacturing the same of the invention, at least a part of the second magnetic layer portion or the third magnetic layer portion may be located on an inclined surface formed of the insulating layer. In this case, even if exposure for photolithography for forming the first magnetic layer portion is adversely influenced due to the formation of at least a part of the second or third magnetic layer portion on the inclined surface and thus the corners of the step along the width at the first coupling portion are relatively greatly rounded, a variation in the substantial width of the first magnetic layer portion is avoided.
Other and further objects, features and advantages of the invention will appear more fully from the following description.